Mass production of components, such as gears and the like, typically includes a series of machines integrally linked in a production line. Such machines may include cutters, grinders, shavers, heat treat and the like. Generally, a raw component is loaded at the beginning of the line and each machine performs a specific manufacturing process on the raw component, ultimately producing a finished product. Each step of the process includes an associated cycle-time. The cycle-time is the amount of time it takes a particular machine to perform its process, including loading and unloading of a component. The cycle-time translates directly into manufacturing costs and thus component price.
In addition to cycle-times, each machine has associated costs. The initial cost is the capital investment required to purchase the machine. Other costs are incurred throughout the life of the machine. These on-going costs include maintenance, replacement parts, general running costs (electricity, lubricant, etc.) and the like.
Gear hobbing is one of a variety of methods employed for manufacturing gears and is generally used in mass production for rough cutting teeth in gear blanks. In gear hobbing, the cutting tool is termed a “hob”. Generally, hobs are cylindrical in shape and are greater in length than in diameter. The cutting teeth of a hob extend radially from the cylindrical body and follow a helical path about the hob, along the length of the hob. Hobbing is a continuous process in which the hob and gear blank rotate in timed relation to one another. The cutting action is continuous in one direction until the gear is complete.
The hob is fed across the circumferential face of a gear blank at a uniform rate. As the hob moves across the circumferential face of the gear blank, both the hob and the gear blank rotate about their respective axes. As the hob cuts the gear blank, tooth profiles gradually form within the circumferential face of the blank and the teeth gradually take shape across the gear face.
Accuracy and production requirements dictate the type of hob to be used. Hob types vary from single-thread to double-thread or more in multiple. A single-thread hob makes one revolution as the gear being cut rotates the angular distance of one tooth and one space. For example, for producing a spur gear having 49 teeth, a single-thread hob rotates 49 times for one revolution of the gear blank. Similarly, when using a double-thread hob, the hob rotates 49 times for two revolutions of the gear blank. Multiple threads increase the rotational speed of the gear blank accordingly. However, certain limitations are inherent in using multiple-thread hobs.
The number of threads is a function of the intended purpose. Although not efficient for mass production, single-thread hobs may be used for both roughing and finishing. Multiple-thread hobs are commonly used for roughing. As a result of the multiplication effect of multiple-thread hobs, speed increases, thus providing savings in cycle-time. However, compared to single-thread hobs, multiple-thread hobs leave much larger feed marks on the tooth profiles of the gear teeth. For example, using a single-thread hob, each tooth of the hob cuts every tooth space in the gear blank. A double-thread hob contacts every other tooth space during any single revolution of the gear blank.
Various feed directions of the hob, relative to the gear blank, are employable and are dependent upon the type of gear to be cut. The hob feed directions include axial, oblique, infeed (or plunge) and tangential. Generally, the hob is fed into contact with the gear blank as opposed to the gear blank being fed into contact with the hob. Axial hob feeding includes the hob being fed into the gear blank along a path that is parallel to the axis of rotation of the gear blank. In oblique hobbing, the hob path is at an angle relative to the axis of rotation of the gear blank. In this manner, the cutting action is distributed along an increased length of the hob as it is fed across the gear blank. In infeed hobbing, the hob is fed radially inward into the gear blank. With tangential hobbing, the hob is fed tangentially across the gear blank.
Besides rough forming of gear teeth, other forming processes may be required for a particular gear design. For example, typical gear designs dictate that a chamfer be formed on each side of the individual gear teeth. To achieve this, a second roughing process is required using additional tools and machines. Generally, a chamfering tool is used and includes a circumferential face having a set of mating gear teeth recessed between chamfer forming faces. The rough gear and tool are pressed into engagement with one another, wherein the rough gear blank meshes with the mating gear teeth of the chamfering tool and both the tool and the rough gear rotate in unison. As the rough gear and chamfering tool rotate, the chamfer forming faces displace material at each side of the individual gear teeth, thus forming a chamfer on each side of the individual gear teeth.
Having thus formed the chamfers, the displaced material must be removed from the rough gear in a process known as deburring. Deburring of the rough gear is typically achieved using a third process that implements a third tool for cutting away the displaced material. It is, however, known in the art to combine the chamfer forming and deburring tools. A single chamfer/debur tool is constructed similarly as described above for the chamfer tool, however, further includes cutters associated with the chamfer forming faces. The cutters remove the displaced material immediately after the corresponding forming face forms the chamfer.
To finish the gear, a finishing process is performed. Gear finishing processes are used for improving accuracy and uniformity of the gear teeth. The degree of accuracy and, thus, the finishing process required is dependent upon the functional requirements of the gear.
Gear shaving is the most commonly used method of finishing gear teeth prior to hardening. Gear shaving is a cutting process, whereby material is removed from the profiles of each gear tooth by a cutter. The cutter may vary in form, typically resembling a gear or rack depending upon whether a rotary or a rack gear shaving method is used.
Typical gear production lines include a series of machines for performing each of the above-described processes. As such, each machine requires an initial capital investment cost and the other associated costs described above. Furthermore, general production cycle-time of a production line, having multiple machines, includes transfer time between machines. Key elements of manufacturing costs include, but are not limited to, the number of machines required, the number of processes required, the set-up time between the processes and the overall cycle-time of each work-piece. As manufacturers seek to improve overall operational costs reduction in any one of these areas is sought. Manufacturers seek to reduce the amount of machines required for production, thereby reducing capital and maintenance costs, as well as reducing the cycle-time for producing each component, thus increasing the efficiency of the complete process.
A majority of state-of-the-art machine tools are computer numerically controlled machines or “CNC” machines. Such machines use computer control for both machine operation and set-up. Computers further enable a series of machines that perform separate functions to work in concert to perform several operations on a work piece and to mass produce final products. Each machine, however, must be independently programmed by an operator prior to processing a new work piece design. Because each machine is independently programmed, set-up time and thus, overall manufacture time is less efficient than desired. As a result, overall manufacture cost and product cost is higher than desired.
Therefore, it is desirable in the industry to provide improved machinery for producing components, such as gears. The improved machinery should limit the need for additional, supporting machines, reduce the overall capital investment and maintenance costs, as well as reduce the cycle time of component manufacture.